Field of the Invention
The present invention relates to an automatic transmission for a vehicle. More particularly, the present invention relates to a planetary gear train of an automatic transmission of a vehicle that improves power delivery performance and reduces fuel consumption by achieving nine forward speed stages using a minimum number of constituent elements.
Description of Related Art
In recent years, a rise in oil price caused unlimited competition for enhancing fuel efficiency.
As a result, researches into reduction of weight and enhancement of the fuel efficiency through down-sizing are being conducted in the case of an engine, and researches for simultaneously securing operability and fuel efficiency competitiveness through multistages are conducted in the case of an automatic transmission.
However, in the automatic transmission, as a number of transmission steps increases, the number of internal components increases, and as a result, mountability, cost, weight, transmission efficiency, and the like may still deteriorate.
Accordingly, development of a planetary gear train which may bring about maximum efficiency with a small number of components may be important in order to increase a fuel efficiency enhancement effect through the multistages.
In this aspect, in recent years, 8-speed automated transmissions have tended to be achieved and the research and development of a planetary gear train capable of implementing more transmission steps has also been actively conducted.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.